LAND attack threat 'not significant', says Microsoft

French alert doesn't stack up to much, apparently

Microsoft has rejected the seriousness of a security warning about its software. On Tuesday the French Security Incident Response Team (FrSIRT) issued an alert about a security bug in Microsoft's implementation of TCP/IP in Windows XP and 2003.

The flaw in the Windows IPv6 TCP/IP stack means systems are liable to crash when processing maliciously crafted packets in which the SYN flag is set, and the source address and port are the same as the destination address and port (a so-called Land Attack). FrSIRT said that even systems running the latest, fully patched versions of XP SP2 or Win 2003 SP1 could be crashed using an attack based on the vulnerability.

Microsoft disputes this point, arguing that customer running XP SP2 or Win 2003 SP1 or those who'd applied a patch release in April (MS05-019) are protected. No customers have reported attacks based on the reported vulnerability, it says. "We do not consider this to be a significant threat to the security of the Internet. This is similar to other TCP connection reset issues," it said in an advisory published Wednesday, 18 May.

According to FrSIRT, Microsoft's April fix only addresses a variant of the latest vulnerability, an IPv4 Land attack risk, not the IPv6 attack that formed the subject of its Tuesday alert. It advises corporates to filter potentially malicious traffic at the firewall pending a more comprehensive fix. ®